Amiga Demo's

I've had much the same thoughts. I'd love to do it the 'classic' way (I assuem the origianl teletext encoders used for CEEFAX (BBC) and ORACLE (ITV) were built from TTL or simialr). Alas I cna't believe schematics of those exist anywhere I could get at :-( Of course the decoder was simplified by the fact that there were many TVs that had teletext decoders built-in (no point in transmitting somehtign if nobody can decode it). So there were semi-custom chips and chipsets to decode teletext. There was ther TIFAX board (from TI, not supriisngly) which ued some pertty-much undocumetned ICs (including something called a 74S262, which is not in many TTL books, but is in fact a character gnerator ROM). And the Philips chipsets which had excellent data sheets and applciation notes. The oriignal one (SAA5000 series) was something of a pain to use with a computer (but it;s what the Acorn teletext decoder used, and in fact the BBC micro has an SAA505 IC on the mainboard (this being the character geneator ROM, etc, of the chipset) so it could display teletext correctly. The later Philips chipsets (SAA5240, etc) were much nicer to use with a computer because they were controlled by an I2C bus which was used not only to select which teletxt page to display, but also could read/write any byte of the display memory. So you could select a page using I2C, check it had arrived (flag readable over I2C) and then read it out using the I2C bus. The Morley teletext decoder for the BBC micro is little more than a TV tuner/IF strip, the SAA5240-based decoder and a CITAC (Computer Interface for Tuning and Control), another I2C-controlled device for channel selection, etc. The whole thing is controlled by a couple of lines on the BBC user port, it-banging the I2C protocol. (can you tell I have one of these? darn it, I have scheamtics...) I can't rememer what the bit-rate is, but IIRC it's aroudn 6MHz. Not hard to do. -tony